If the amino acid sequence of the desired protein is known, the DNA code can be worked out and the DNA made in the lab by stringing together the correct order of nucleotides.

Note:Many proteins are extremely large, therefore this would be a tedious process.

Isolate the messenger RNA (mRNA) for the desired gene and make a single copy of the complementary DNA using the enzyme reverse transcriptase and another copy is made by adding DNA polymerase so that a doubled stranded length of DNA is made. (The original reverse transcription enzymes were first discovered in retro viruses.)

Isolate the gene from the entire genome. To do this the DNA must first be cut into fragments and the one containing the desired gene must be identified. The enzymes used to cut the DNA are called restriction enzymes or restriction endonucleases.

There are many restriction enzymes (R.E), each one of which will cut at a specific DNA sequence.

The names of the restriction enzymes indicate from where the enzyme was isolated. (For example, EcoR1 comes from E.coli.)

The target sites are palindromic (reads the same both ways, like "Hannah" or "Madam") and may cut at the same place in both strands creating blunt ends as in Hpa11 or at different places in the 2 strands leaving so-called sticky ends as in EcoR1.